1. Field of the Invention
The present invention relates to an ink cartridge for storing and supplying ink to a printer and, in particular, to an ink jet printer.
2. Description of the Related Art
An ink cartridge supplies ink to a printing head which ejects droplets of ink. The ink cartridge includes an ink holding member arranged in an ink container made from a porous material such as urethane foam, to prevent occurrences of air bubbles and ink leakage which might occur when the ink is moved in the ink cartridge.
A proposal has been made in the prior art that ink is held in the ink holding member by capillary attraction so that an appropriate negative pressure level is maintained in the ink container (for example, U.S. Pat. No. 4,771,295).
For example, FIG. 10 in the attached drawings shows a conventional ink cartridge designed to move ink towards an ink supply hole in the ink cartridge. In FIG. 10, the ink cartridge comprises a generally rectangular parallelepiped ink container 50 having a top wall 51 with a vent hole 52, a bottom wall 53 with an ink supply hole 54, and side walls 55 between the top wall 51 and the bottom wall 52. The top wall 51 includes ribs 56 on the inner surface thereof. An ink holding member of a porous material 57 is arranged in the ink container 50 in abutment with the bottom wall 53, the side walls 55 and the ribs 56 under pressure.
A tubular projection 58 extends in the ink container 50 to form the ink supply hole 54 and to locally compresses a portion of the ink holding member 57. A filter 59 is arranged on the top of the tubular projection 58, and a member 60 which is a part of a printing head of a printer is connected to the ink supply hole 54 to eject droplets of ink. In this arrangement, a portion of the ink holding member 57 located near the ink supply hole 54 has a higher fiber density than that of the remaining portion, so a capillary attraction force is greater at that portion of the ink holding member 57 near the ink supply hole 54 than a capillary attraction force at the remaining portion, whereby ink is gathered near the ink supply hole 54. However, this ink gathering action is not effective in the entire ink holding member 57, and ink located at a position remote from ink supply hole 54 can remain unconsumed. In addition, the provision of the tubular projection 58 extending in the ink container 50 reduces the available volume of the ink container 50, leading to a lower volumetric efficiency.
In addition, if the ink cartridge is integrally connected to the printing head, it is necessary to replace the ink cartridge together with the printing head when the ink in the ink cartridge is consumed. The printing head is more expensive than the ink cartridge, and the cost of the print cartridge increases.
An ink cartridge adapted to be removably connected to a printing head is disclosed in, for example, Japanese Unexamined Utility Model Publication (Kokai) No. 63-176635. FIG. 11 in the attached drawings shows a conventional ink supply device including an ink cartridge 50a removably connectable to a printing head 60a. The ink cartridge 50a has a plug member 61 of an elastic material arranged in an ink supply hole 54a. The printing head 60a has a hollow needle 62 at a position corresponding to the plug member 61.
When the ink cartridge 50a is connected to the printing head 60a, the hollow needle 62 passes through the plug member 61 to allow ink to flow from the ink holding member 57a through the hollow needle 62 to an ink reservoir 63 in the printing head 60a. It is then possible to remove the cartridge 50a from the printing head 60a by drawing the hollow needle 62 from the plug member 61. Therefore, it is possible to replace only the ink cartridge 50a when the ink is consumed and to reduce the cost of the print cartridge. However, it is necessary to provide guide means or positioning means when the ink cartridge 50a is connected to the printing head 60a, resulting in a complex structure. In addition, if the hollow needle 62 is contaminated with dust at its tip or peripheral surface, dust may enter the ink cartridge 50a and may clog the ink passage in the hollow needle 62 or the ink passage in the printing head 60a.